Field of the Invention
This invention relates to a method for preparing highly basic carbonate overbased calcium sulfonates useful as detergent additives n lubricating oils for internal combustion engines. More particularly, it relates to a method for preparing highly basic calcium sulfonates having metal ratios of at least about 10 and preferably about 12 to 15 which method comprises the steps of: (1) forming an initial mixture of a lower molecular weight alkanol, an alkyl or alkaryl substituted sulfonic acid or sulfonate compound, a diluent and a solvent; (2) adding a basic calcium compound to the initial mixture to form a second mixture in which the amount of added calcium is at least about ten times the amount necessary to form a neutral calcium sulfonate; (3) heating the second mixture to reflux temperature; (4) carbonating the second mixture at said reflux temperature to form a carbonated product while simultaneously and continuously removing water produced by the carbonation reaction; (5) after carbonation is stopped, heating the carbonated product to an elevated temperature sufficient to remove the alkanol; and (6) removing solids and solvent from the carbonated product.